The present invention relates generally to the devices, systems and methods of detecting increased fluid levels in tissue, and particularly to devices, systems and method of detecting increased fluid levels associated with extravasation in tissues and controlling powered injectors in response to such detection.
The following information is provided to assist the reader to understand the invention disclosed below and the environment in which it will typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the present invention or the background of the present invention. The disclosure of all references cited herein are incorporated by reference.
Elevated fluid levels in tissue can arise as a result of introduction of a fluid into the body, for example, during an injection procedure. In that regard, in many medical diagnostic and therapeutic procedures, a physician or other person injects fluid into a patient and, particularly, into a patient's blood vessels. Moreover, in recent years, a number of injector-actuated syringes and powered injectors for pressurized injection of contrast medium in procedures such as angiography, computed tomography, ultrasound and NMR/MRI have been developed. Such pressurized injectors can also be use in the delivery of therapeutic agents.
Extravasation or infiltration is the accidental infusion or leakage of an injection fluid such as a contrast medium or a therapeutic agent into tissue surrounding a blood vessel rather than into the blood vessel itself. Extravasation can be caused, for example, by rupture or dissection of fragile vasculature, valve disease, inappropriate needle placement, or patient movement resulting in the infusing needle being pulled from the intended vessel or causing the needle to be pushed through the wall of the vessel. High injection pressures and/or rates of some modem procedures can increase the risk of extravasation. In computed tomography, for example, contrast injection flow rates can be in the range of 0.1 to 10 ml/s.
Extravasation can cause serious injury to patients. In that regard, certain injection fluids such as contrast media or chemotherapy drugs can be toxic to tissue. It is, therefore, very important when performing fluid injections to detect extravasation as soon as possible and discontinue the injection upon detection.
Several extravasation detection techniques are known in the art. Two simple and very useful techniques for detecting extravasation are palpation of the patient in the vicinity of the injection site and simple visual observation of the vicinity of the injection site by a trained health care provider. In the palpation technique, the health care provider manually senses swelling of tissue near the injection site resulting from extravasation. By visual observation, it is also sometimes possible to observe directly any swelling of the skin in the vicinity of an injection site resulting from extravasation.
In a procedure involving injection of a fluid that can cause significant harm if extravasation occurs, one can first inject a relatively benign fluid through the needle/catheter and determine if an extravasation of the relatively benign fluid occurs. Published U.S. Patent Application No. 2002/0183613, the disclosure of which is incorporated herein by reference, for example, discloses a method of preventing extravasation of a contrast agent during a computed tomography injection using an automatic injector device. The method includes the steps of establishing the absence of extravasation using an absorbable injectate, such as saline, prior to injecting the contrast agent. The automatic injector includes a computerized injector head capable of switching between two injectates without physical human intervention. During, the method an operator first attempts to position distal end of a percutaneous implement such as a catheter in the vessel such that fluid communication is established between the lumen of the catheter and the vessel. The injector is then instructed to inject saline through the catheter lumen. A determination is then made (via palpation/observation) if an extravasation of the saline has occurred. If it is determined that no extravasation has occurred, the injector is instructed to inject contrast agent. If an extravasation is determined to have occurred during the saline injection, the process steps of repeated positioning the catheter within the blood vessel, injection saline and determining if an extravasation of saline has occurred are repeated.
In addition to palpation and observation, there are a number of automated methods of detecting extravasation that may include automatic triggering of an alarm condition upon detection.
In that regard, several plethysmographic detection techniques are available. For example, mercury strain gauge plethysmographs measure the volume change resulting from venous blood flow in a cross sectional area of a limb of a patient. Air cuff or pulse volume recorder plethysmographs measure the changes in pressure within a recording cuff. Such plethysmographs can be cumbersome to operate and/or insensitive to small changes in volume.
Impedance plethysmographs use low-frequency electromagnetic energy transmitted via galvanic contact with the skin to measure changes in the electrical impedance in a defined tissue volume of a limb. Detection of extravasation via impedance changes is disclosed, for example, in U.S. Pat. Nos. 5,964,703 and 5,947,910, the disclosures of which are incorporated herein by reference. In this method, an impedance change of a certain level relative to a baseline measurement in the vicinity of the injection site is interpreted as being an extravasation. A change in impedance occurs during extravasation because injection fluid in the tissue of the patient changes both the volume and the electrical impedance properties of the tissue. Use of electrodes in impedance plethysmographs can, however, result in instabilities. For example, maintaining suitable electrical (ohmic or galvanic) contact between the electrodes of impedance plethysmographs and the skin of the patient is often very difficult.
Photo-plethysmographs measure the optical scattering properties of capillary blood to detect the presence of extravasated fluids in tissue. An example of a photo-plethysmograph is described in U.S. Pat. No. 4,877,034, the disclosure of which is incorporated herein by reference. Because light is heavily absorbed in tissue, however, the sensitivity of photo-plethysmographs is generally limited to the top ¼ inch of tissue. Many extravasations, however, occur deeper than ¼ inch. Moreover, the injection medium may flow into interstitial spaces remote from the photoplethysmograph sensors and go undetected.
A number of extravasation detection devices attempt to measure temperature differences to determine if an extravasation has occurred. For example, U.S. Pat. No. 4,647,281 discloses subcutaneous temperature sensing of extravasation to trigger an alarm. In this method of extravasation detection, an antenna and a microwave radiometer instantaneously measure the temperature of the subcutaneous tissue at the site where fluid is injected by measuring microwave radiation emitted naturally from the body. An algorithm periodically determines the temperature difference between tissue and injected fluid, and compares the difference to a fixed threshold. An alarm processor uses the comparison to determine an alarm condition.
In addition, U.S. Pat. No. 5,334,141, the disclosure of which is incorporated herein by reference, discloses a microwave extravasation detection system employing a reusable microwave antenna and a disposable attachment element for releasably securing the microwave antenna to a patient's skin over an injection site. The attachment element holds the antenna in intimate contact with the patient's skin to optimize microwave transfer therebetween, while shielding the antenna from environmental noise signals. U.S. Pat. No. 5,954,668, the disclosure of which is incorporated herein by reference, also discloses use of a microwave antenna to sense temperature of tissue to detect extravasation. Although measurement of temperature changes and emissivity using microwave energy can result in instantaneous detection, temperature differences are often too small for practical measurement.
Published U.S. Patent Application Publication Nos. 2003/0036674 and 2003/0036713 and Published PCT International Patent Application Nos. WO/2003/009753, WO/2003/009752 and WO 2005/043100, assigned to the assignee of the present invention, the disclosures of which are incorporated herein by reference, disclose transmitting and receive antenna elements, sensing methods and processing algorithms suitable for the detection of elevated fluid levels (including those caused by extravasation) using active transmission of microwave energy into tissue. The studies of sensors incorporating such antenna elements have shown that electromagnetic energy having, for example, a frequency in the range of approximately 300 MHz to approximately 30 GHz (and, more preferably, in the range of approximately 1 GHz to approximately 10 GHz, and, even more preferably, in the range of approximately 3 GHz to approximately 5 GHz) provides good penetration into tissue. Such electromagnetic energy is launched into the subcutaneous tissue and a resultant signal is measured. Electromagnetic energy in the frequency range set forth above has been found to transmit through the skin and to transmit or propagate well within, for example, fat. Good transmission through the fat layer is beneficial for detection of extravasation as many extravasations occur in the fat layer.
It is desirable to develop improved devices, systems and methods of detecting and preventing extravasation.